According to the prior art, use is made of injection devices whose injection jets exhibit a reduced or small penetration depth into the combustion chamber. In practice, it has however been found that, despite a reduced penetration depth, the combustion chamber internal walls are wetted with fuel, specifically even if the injection jets do not directly strike the combustion chamber internal walls. Charge movement in the combustion chamber may be the cause of this is non-evaporated liquid fuel that, in the form of fuel droplets, is transported to the combustion chamber internal walls, and wets these.
The prior art has also disclosed concepts in which the cylinders of the internal combustion engine are each equipped with an injection nozzle in the region of the cylinder liner. The injection nozzle of a cylinder is in this case oriented toward the cylinder head and in some cases toward the outlet valve of the cylinder. This feature is intended to assist and accelerate the evaporation of the fuel particles or fuel droplets and thus the mixture formation. At the same time, the head and the closed outlet valve are cooled by way of fuel. It is also sought in fuel injection systems to reduce pollutant emissions. It is also possible for two injection nozzles to be provided in the region of the cylinder liner, whereby it is sought to further increase mixing of the air-fuel mixture. U.S. Pat. No. 5,421,301 describes such an internal combustion engine.
A disadvantage of the injection method described in U.S. Pat. No. 5,421,301, and generally of internal combustion engines whose cylinders are equipped with an injection device in the region of the cylinder liner, is that an injection can be performed only when the cylinder-specific piston, on its path toward bottom dead center, has passed the injection device and makes the combustion chamber accessible to the openings of the injection device. The crank angle window, in which an injection can be performed, is thus restricted. This is all the more relevant because, in the case of a direct injection, it is inherently already the case that very little time is available for the mixture formation.
An injection nozzle which is oriented toward the cylinder head, as described in U.S. Pat. No. 5,421,301, supplies fuel only to the cylinder-head-side region of the combustion chamber during the course of the injection process, whereas the region of the combustion chamber between the injection device and bottom dead center, that is to say the piston-side region of the combustion chamber, remains disregarded during the injection.
Against the background of that stated above and recognizing the aforementioned problems the inventors have developed a method for operating a fuel injection system to resolve at least some of the problems. In one example, the method includes injecting fuel from a first direct fuel injection device arranged in a cylinder liner in a cylinder block into a combustion chamber and injecting fuel from a second direct fuel injection device arranged in a cylinder head into the combustion chamber, the first and second direct fuel injection devices arranged at an obtuse angle with regard to an intersection of central axes of the first and second direct fuel injection devices. Injecting fuel into combustion chamber with injection devices arranged at an obtuse angle with regard to one another enables the fuel jets interact with one another to increase air-fuel mixing and decrease wall wetting within the combustion chamber. Consequently, combustion efficiency is increased and emissions are correspondingly reduced. In one example, the first direct fuel injection device may be positioned on an exhaust side of the combustion chamber in the cylinder liner and the second direct fuel injection device may be positioned between an intake valve and an exhaust valve in the cylinder head. When the fuel injection devices are arranged in this way the fuel spray from the devices may interact with one another and the intake airflow to increase tumble and/or swirl airflow patterns in the intake airflow. Consequently, mixing of the air-fuel mixture may be further increased, thereby increasing combustion efficiency.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.